smart city development, challenges, and applications. Further, we review common security attacks on blockchain and security improvement solutions and the directions for future research.
Keywords: Blockchain, smart city, security, privacy, Internet of Things
1.1 Introduction
Blockchain has gained tremendous popularity in recent times because of its fundamental properties and peer-to-peer operations. Blockchain theory was the future of well-known researcher Santoshi Nakamotos in 2008 with Bitcoin crypto-currency innovation. More than 2,500 crypto-currencies exist, but the authentic utilization of Bitcoin is still not explored effusively. Various issues like secure document transferring, anti-money laundering, decentralization, and authorized and unauthorized mining actions are near related to Bitcoin [1–5]. The Bitcoin system model nearly takes 5 to 8 minutes for the mining process and validation of the transaction, which plays a crucial role in numerous appliances such as industry, economics, supply chain management, healthcare, and the Internet of Things (IoT). In present situations, digital information streams from one-end to a new dissimilar end via an unauthorized transmission channel. Where securities models and privacy are the two significant worries in any transaction, blockchain produces a protected peer-to-peer broadcast. Moreover, all the transactions of blockchain publicly accessible for analyzing although none can amend the transaction one time it is recorded [1–6].
Blockchain is a scattered data catalog that monitors an emergent directory of transaction reports with systematizing them into a hierarchical series of blocks because of database management. Coming to safety potential, blockchain builds and maintains with peer-to-peer overlie setup and secured with intellectual, decentralized exploitation of cryptography techniques. Experts forecasted that blockchain-related annual revenue would reach approximately 22 billion dollars at the end of 2030, with an annual growth rate of 29.6%. Numerous distinguished organizations like Accenture, Cisco, Morgan Stanley, Google, Citibank, Ali baba, IBM and IT vendors, financial consultancies, and internet giants designed and developed a high-standard research laboratory to make a capital layout blockchain knowledge [3–6]. Moreover, blockchain with Artificial Intelligence (AI), Machine Learning (ML), and big data are considered the heart of computing skills for the upcoming generation financial inducts. A few governments have released methodological reports along with white papers on blockchain utilization for a positive approach. Some of them like the European Central Bank unconfined credentials on distributed ledger expertise, and the UK government liberated a fresh testimony that illustrates the outlook of distributed ledger technology. The Chinese administration liberated white papers on the blockchain tools besides improvement in China; the USA builds an authorized and authoritarian background for blockchain knowledge development. In academe, several documents are available on blockchain in the earlier period, consist of a dozen of the article, and provide information on safety then secrecy risks of blockchain. Furthermore, most of the safety then secrecy risk–based articles of blockchain-focused on uncovering attacks that suffer blockchain, and some target specific proposals for employing some current countermeasure adjacent to a subset of various attacks. Among these, very few attempts describe a complete investigation of the safety then confidentiality characteristics of blockchain along with different protocol implementation methods [2–8].
1.2 Blockchain Preliminaries
1.2.1 Functioning of Blockchain
Blockchain is a collection of heterogeneous distributed networks. It considers as a unique technology of this century among other famous innovations because of its elements like crypto techniques, consensus algorithms, and public ledger; working procedure of blockchain consists of various styles, among those we mentioned some of them: customer, client, or node who desire to make a transaction will record and broadcasts the data to the appropriate setup, next to the receiver or the node who interest to receive the data validate the genuineness of data received, and after validation stores data in a block inside the network, every node or the customer in the network authorize the transaction through implementing the PoW or else PoS algorithms which need the validation, and finally, the network that utilized the consensus models will be stored into the block and connected to the blockchain list. Then, every single node in the setup acknowledges the relevant block and then enlarges the chain position on block.
1.2.2 Design of Blockchain
The expansion of the blockchain system will make tremendous changes and impact approximately every industrial, educational, and scientific field in the coming days. In particular, financial transactions are progressing in inventive ways, making it exceptionally important for one and all to understand the blockchain mechanism’s architecture and working style. Blockchain blocks are continuously enhance, secure with crypto techniques [6–10]. Here, each block holds a crypto-based hash value of the preceding block, a timestamp, along with transaction info.
In the design of blockchain, information or records are professional along with a related listing of transaction blocks well-maintained in a balanced catalog in the pattern of smooth files. Each block, linked with the preceding block, the initial block entitled the source block. The blockchain database visualized as a good stack, blocks mounded on the peak of one another, finished as the initial block as the stack’s base. Every block of blockchain authorized with cryptography has a function by implementing the SHA-256 algorithm and stored in the block’s header. One parent block can hold multiple children block; every child block encloses some parent hash value. The characteristics of child blocks purely depend on the parent block’s identity and properties. This procedure prolongs until getting each grandchild blocks [6–12]. The cascade consequences confirm that, just once a block has several productions, it cannot interfere with all the successive blocks’ forceful recalculations. For more understanding, we mentioned some ingredients with more explanations [4–16].
1 i. Data: In blockchain, data stored in the database mostly depend on the respective services and applications, like recording the transmission particulars and banking with IoT. They were storing if data performed peer-to-peer, cloud formation, etc.
2 ii. Hash: In the hash function, we can give any length message as input, but it produces unique predetermined length output. If any assailant made changes in the message, then the output comes out entirely differently. For example, if anyone client makes an effort to modify the info kept in a block, then afterward, the block shows an entirely different hash value. To avoid this kind of situation, there must be an assurance that minors of the network must have the knowledge prepared by revising the ledger replicate of total abusers. This will surely boost the reliability of info kept in the blockchain.
3 iii. Timestamp: For every transaction, it is compulsory to note the time once the block is shaped. Timestamping is a technique employed to trail or to follow the formation or else adapt the period of a certificate in a safe mode. This kind of procedure turns into a vital tool in the corporate business world. Moreover, blockchain authorizes only the concerned parties to recognize the source and then accessibility of a certificate/file on a specific day and occasion.
4 iv. Moreover, the data contains nonce and digital signatures; each customer holds both public/private keys. Digital signature restrains both keys for signing (private key reserved, sign-on, transaction data) and verification (public key for validation and decrypt the data) phase. Nonce value with 4-byte strength utilized for message authentication.
1.2.3 Blockchain Elements
Blockchain collects different techniques like mathematical methods, algorithms, cryptography protocols, and economic standards. It merges every part of end-to-end networking plus distributed consensus algorithm to resolve the management issues from a long-established scattered database. As we mentioned earlier, blockchain contains numerous elements; out of them here, we discussed some important points below [4–10, 12–18].
1 i.
